ORTHODOXY AND THE HOLY ROSARY from Orthodox Wiki ~
The prayer rope was formed by St. Pachomius in the fourth century. From there the rosary developed, some say as early as the eighth century. It is said that even centuries later St. Seraphim of Sarov (1754-1833) used it to pray to the Virgin Theotokos. In the thirteenth century, Roman Catholics started using in the West following its discovery by Dominic de Guzmán, a Spanish priest.
“…Say the 0 Hail, Mother of God and Virgin one hundred and fifty times… This rule was given by the Mother of God herself in about the eighth century… We Orthodox have forgotten about it, and St. Seraphim has reminded me of this Rule. In my hands I have a hand-written book from the cell of St. Seraphim, containing a description of the many miracles which took place through praying to the Mother of God and especially through saying one hundred and fifty times the O Hail, Mother of God and Virgin… Whomever he spoke to about this miracle-working Rule remained grateful to him…”.
Orthodox Method :The prayers said on this form of the prayer rope are the Hail Mary (also Hail Mother of God and Virgin), the Lord’s Prayer, and the Jesus Prayer. The Hail Mary is said in groups of ten, and in between each group of ten are said the Lord’s Prayer and the Jesus Prayer. Between each grouping of Hail Marys, a meditation is also pronounced, which is then thought of throughout the succeeding Hail Marys.